1. Field of the Invention
The present invention relates to an exhaust gas recirculation system of an internal combustion engine.
2. Description of Related Art
Internal combustion engines typically include an exhaust gas recirculation (EGR) system to recirculate a controlled portion of the engine exhaust gas into an engine intake manifold in order to provide a reduction in NO.sub.x emissions. Typically, a control mechanism including an EGR valve is provided to vary the EGR rate according to one or more sensed conditions, such as engine temperature, air charge entering the intake manifold, and engine speed. A stepper motor driven EGR valve has been employed in an exhaust gas recirculation system wherein stepper motor steps are calculated primarily as a function of engine speed and air charge. Such control of the stepper motor produces errors in the control of the EGR valve as a result of variations in ambient barometric pressure and temperature.
An object of the present invention is to provide an EGR system with improved control of a stepper motor driven EGR valve